Microelectronic position sensor for volume control

ABSTRACT

A microelectronic position sensor having a stationary base portion including magnetic field sensitive elements and an adjustment means rotatably mounted within the adjustment means and including a permanent magnet; the adjustment means being electrically coupled to the apparatus by means of a plurality of electrically conductive terminals embedded in the adjustment means; the adjustment means including an integrated circuit on which the magnetic field sensitive elements are mounted for providing an electrical signal depending on the position of the permanent magnet and the rotor; the adjustment means and the stationary base portion include housing parts having interengaging flanges and forming together a self-contained unit encompassing the electric and magnetic components of the position sensor and in which the adjustment means is rotatably mounted on the stationary base member; a soft-iron member is mounted in the stationary base member to form an iron return path in the magnetic system comprising the permanent magnet and the magnetic field sensitive elements; and the electrically conductive contact between the terminals and the integrated circuit is effected by bonding to the integrated circuit, each terminal being separately secured to the integrated circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a microelectronic position sensor, e.g for usein hearing aids and the like for volume control, function shifts orchanges of another adjustable parameter of the associated apparatus,said position sensor operating by means of magnetic field sensitiveelements and comprising a stationary base portion or stator whichcontains magnetic field sensitive elements and an adjustment means orrotor which is rotatably mounted and contains a permanent magnet, andwherein the stator is electrically coupled to the associated apparatusby means of a plurality of electrically conductive terminals which areembedded in the stator, said stator comprising an integrated circuit onwhich the magnetic field sensitive means are arranged for providing anelectrical signal depending on the position of the permanent magnet andhence of the rotor.

2. Related Art

A position sensor of the above mentioned type is disclosed in U.S. Pat.No. 4,415,856. This prior art sensor has its rotor mounted through anaperture in a panel of a housing. The stator integrated circuit placedin a dual-in-line package (DIP) is mounted on a printed circuit board inthe housing below the rotor. Such DIP member is a standard componenthaving a size of approx. 10×6 mm with a distance between its fourterminals on each side of approx. 2.5 mm. The mutually independentmounting of the stator and rotor implies a considerable distance betweenthe magnet of the rotor- and the magnetic field sensitive elements inthe stator which is detrimental to a reliable and precise operation.This again, however, has the adverse effect of increasing the requiredsize of the permanent magnet for obtaining a sufficient magneticresponse of the sensitive elements. The total height of a sensor of thiskind is large due to the above indicated structural features and thetermination method to be used on the DIP member.

A position sensor of the above mentioned type is, through its integralcircuits, particularly suitable for providing digital output signals,which is important when the remaining circuits of an equipment areentirely or partially based on such signals. However, this known Halleffect position sensor is not suitable--nor--meant--for microelectronicuse where the outer dimensions of a e.g. for use in hearing aids, shouldnot exceed a magnitude of 3.4 mm, neither in diameter nor in height, andtherefore it does not offer a solution of position sensors of such sizeand having sufficiently accurate operation positions. The same appliesto other known embodiments of Hall effect position sensors or rotaryswitches, cf. e.g. U.S. Pat. Nos. 4054860, 4054861, 4199741, and 4459578and DE patent publication No. DE-A-3908892.

Electronic pulse generators for microelectronic use e.g. in hearing aidsare known from the Applicant's Danish patent applications Nos. 1838/90and 52/91. Although the inventions according to applications relate to adevelopment of such pulse towards an increasingly simple and at the sametime electronically more reliable electromechanical construction, theyare, precisely from a construction point of view, comparatively complexwith the ensuing risks of malfunction during use thereof in hearingaids, and correspondingly costly to produce.

SUMMARY OF THE INVENTION

It is therefore the object of the invention to provide a microelectronicposition sensor, in particular for use in hearing aids and the like,which remedies the above disadvantages of the hitherto known positionsensors or electromechanical pulse generators.

This object is achieved by means of a microelectronic position sensor ofthe type having the following features: a stationary base portionincluding magnetic field sensitive elements and an adjustment meansrotatably mounted within the adjustment means and including a permanentmagnet; the adjustment means being electrically coupled to the apparatusby means of a plurality of electrically conductive terminals embedded inthe adjustment means; the adjustment means comprising an integratedcircuit on which the magnetic field sensitive elements are mounted forproviding an electrical signal depending on the position of thepermanent magnet and the rotor; the adjustment means and the stationarybase portion comprise housing parts having interengaging flanges andforming together a self-contained unit encompassing the electric andmagnetic components of the position sensor and in which the adjustmentmeans is rotatably mounted on the stationary base member; a soft-ironmember is mounted in the stationary base member to form an iron returnpath in the magnetic system comprising the permanent magnet and themagnetic field sensitive elements; and the electrically conductivecontact between the terminals and the integrated circuit is effected bybonding to the integrated circuit, each terminal being separatelysecured to the integrated circuit.

Further advantageous features of the microelectronic position sensoraccording to the invention will appear from the following description.

The microelectronic position sensor according to the invention isparticularly outstanding due to its very simple construction with fewmechanical parts and its surprisingly high degree of operationalaccuracy, all of which is obtained while retaining the very small outerdimensions, about one order of magnitude smaller than the prior artposition sensor initially mentioned.

The position sensor is incorporated as a component of e.g. hearing aidsand the like with full digital control, that is electronic control basedon a computer circuit. It is expected that hearing aids of this typewill become an important object for the future further development ofhearing aids in general. One of the properties of this component withrespect to this use in addition to its mode of operation will be ahighly improved reliability compared to the hitherto known volumecontrols and switches.

Therefore, the component is constructed as a simple magnetic whichcontains only a magnet and an integrated circuit (IC) which is locatedin the magnetic field. The magnetic system may be designed in many ways.Thus, the magnet may be located parallelly with or angularly to theintegrated circuit. The integrated circuit comprises a serial data linewhich, via a single electrical connection, transmits binary figurescorresponding to 0 and 1 which, in turn, correspond to low and highvoltages. The incorporation of a computer into a hearing aid permits thecomputer to carry out comparatively complex operations on the basis of asimple input signal via the serial data line. The position sensorprovides a signal in the form of a code (a number) corresponding to therotor position relative to the stator whereupon the computer convertsthe signal to the desired adjustment of the hearing aid, be it volumecontrol, switch of program, tone control, mode shift or the like.

The rotor with the incorporated permanent rod- or disc-shaped magnet maybe freely rotated manually over 360° on the stator whereby the magnetinfluences on the circuits of the integrated circuit in the stator so asto allow the integrated circuit to determine the instantaneous positionof the rotor. If desired, the stator may be provided with a mechanicalstop for the rotation of the rotor. The rotor and stator mayconveniently be made of a moulded plastics material. The componentappears with the built-in integrated circuit as an active componentwhich requires an energy supply usually with a supply voltage higherthan or equal to 1 V and having a tolerance of up to 5 V and a ripple of±0.3 V with a ripple frequency of less than 2000 Hz. Therefore, thecomponent is usually provided with three terminals for this purposewhich are embedded in the stator, viz the line whereupon data from thecomponent to the computer of the hearing aid is transmitted and thepositive and negative battery voltage. The signalling could also beeffected as a current or voltage modulation on the power supply line. Inthat case the component could be made to operate with two connectionsonly.

It is often necessary to adjust the supply voltage in microelectronicdevices. However, a control of the battery voltage may often onlypartially be incorporated in the integrated circuit which shouldtherefore be supplemented with an external capacitor having its ownterminal. Thus, the component has a further terminal, i.e. normally atotal of four terminals which are electrically conductively connected tothe integrated circuit.

Following mounting of the terminals on the integrated circuit, thelatter may be embedded into the stator.

The integrated circuit also comprises a number of magnetic fieldsensitive elements consisting of a magnetic field effect transistor(MAGFET) having two or more drains for splitting the current in theindividual MAGFET, such splitting permitting measurement of thedifferential current between the terminals of the elements when, bymeans of the permanent magnet of the rotor, a magnetic field isestablished perpendicular to the element. Measurement of thedifferential current presents an advantage as to the noise-level of thecomponent compared to measurement of voltage in a Hall element and,likewise, the use of e.g. three drains provides an improved sensitivity.

The determination of the rotor position relative to that of the statorby means of the integrated circuit is effected either digitally oranalogly.

In the digital solution, the magnetic field sensitive elements orsensors in the integrated circuit are arranged on a circle and in anumber corresponding to the desired angular resolution whereupon thesignals from the individual sensors are compared by means of a number ofcomparators so as to generate a series of digital signals from thecomparisons which, by use of a digital decoding circuit, are convertedto digital codes. The inconvenience associated with the digital solutionis the positioning of many sensors, e.g. 64, with correspondingconnections to obtain a desired angular resolution, on a circle in theintegrated circuit. The advantage associated with the digital solutionconsists in fast and simple measurements with the exclusive use ofcomparators.

In the analog solution, the magnitude of the magnetic field is measuredwith one or more sensors which provide(s) an analog signal depending onthe position of the permanent magnet and which may consequently be usedfor the position determination.

A sensor provides a signal which is approximately linearly depending onthe relevant applied magnetic field. The magnetic field varies with therotor position and if there is to be proportionality between the signaland the rotational angle, the magnetic field should vary linearly withthe angle.

With only one sensor it is impossible to obtain an unambiguous relationbetween signal and position. When the rotor and thus the magnet isrotated 360°, the field will vary from a minimum value to a maximum andback again. Therefore, the same field strength will occur for twopositions of the rotor. The lacking information about the position isobtained by means of an additional sensor which senses the field at acertain distance from the first one.

If the field varies sinusoidally, two sensors may advantageously beapplied which are displaced 90° relative to each other and then thesensor is used which, for a given position, provides the most convenientsignal. According to the circumstances, the sensor which provides themost powerful signal is used and which thus reduces the noise problems,or else the sensor which provides the smallest signal and whichconsequently has the highest sensitivity≈largest change of the signalfor a small position change (the sensor with the largest signal providesless sensitivity, the field being here on the flat top at a maximum).

The signal from the sensor is converted by an A/D converter to a digitalcode which may assume a possible number of values corresponding to thegiven number of bits in the code. This presents a problem as it is notknown how large the maximum signal from the sensor will be. Variationsin the magnetic circuit will occur which may give rise to variations inthe maximum magnetic field strength, and differences in the parametersof the electronic circuit may occur.

This means that there is a risk that the codes corresponding to thelargest signals may drop out so that maximum (or minimum) may not be seton the component.

However, there may always be used a suitably wide safety margin, so thatthe signal will be sufficiently large to prevent codes from droppingout. If the variations are wide, however, this margin should besufficiently wide to form, when the signal is at its largest, a largeangle range, in which the A/D converter provides a fixed maximum orminimum value.

The problem of the unknown largest and smallest values provided by thesensor may be solved by using two sensors which are displaced 90°relative to each other and by utilizing the fact that it is guaranteedthat the signal can reach 0.

The sensor which provides the smallest signal is used to provide themeasurement signal. The other sensor is used as a reference, and for theposition determination the value is used which is obtained by divisionof the measurement signal with the reference signal. If the measurementsignal is 0, the reference value will be the maximum. If the angle ischanged slowly the measurement signal will increase and the referencevalue will decrease. In total an increasing value will be obtained whichwill be I when the measurement signal and the reference signal havereached the same level. This corresponds to an angle of 45 relative tothe 0 level.

The reference signal is compared to the measurement signal by means of acomparator and when the measurement signal is the largest the twosignals change roles. A rotation over an angle of 90° from the 0 levelwill generate a signal which varies from 0 at 0° to 1 at 45° and back to0 at 0°. Therefore, this signal cannot be used directly. All codes willappear twice within an angle range of 90°. This ambiguity is resolved byperforming a binary magnitude comparison of the numerical value of themeasurement signal to the numerical value of the reference signal andusing this information to discriminate code segments. This comparisonadds 1 bit to the code.

This ambiguity is resolved by performing a binary magnitude comparisonof the numerical value of the measurement signal to the numerical valueof the reference signal and using this information to discriminate codesegments. This comparison adds 1 bit to the code. In case of a desiredresolution of 6 bits corresponding to 64 positions, the three mostsignificant bits may be derived by magnitude comparison and signmonitoring as explained above. The remaining 3 bits may be derived froman A/D conversion of the ratio of measurement signal to reference signalor reference signal to measurement signal whatever has the leastnumerical value.

The analog solution using the A/D converter presents the advantage thatit is very simple to double the number of codes. This is done byallowing the A/D conversion to be effected with one additional bit. Ifit is desired to have e.g. a seven-bits code for the position, theadditional bit may be introduced simply by using a four-bits A/Dconverter. Such doubling of the number of codes presents certainproblems in the digital solution, e.g. with dimension tolerances.

An increase of the number of codes may provide an increased angularresolution, but an additional advantage associated with the additionalbit is that it may be used for noise suppression. For instance, thecircuit may be so designed that it does not transmit a new position codeuntil one is detected which is a certain value higher than the precedingone or which is different from the two most recently registeredpositions.

According to a particular embodiment, the integrated circuit contains apotentiometer or a variable resistor in addition to the magnetic fieldsensitive elements and the further position determining circuits,thereby making the component appear as a conventional rotarypotentiometer thus allowing use of the component in conventionalmicroelectronic devices without fully digital control.

According to another particular embodiment the integrated circuit inaddition to the magnetic field sensitive elements and other positiondetermining circuits contains an amplifier with variable amplificationfor amplifying electronic signals. The amplification is determined bythe position of the rotor relative to the stator.

Finally, the integrated circuit may comprise a control circuit forsupply voltage so that external control thereof is unnecessary.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in further detail with reference tothe drawings which in a non-limiting manner exemplify an embodiment ofthe invention, and wherein

FIG. 1 is a vertical section through a position sensor and

FIGS. 2 and 3 are exploded views thereof showing the magnetic sensitivecircularly positioned elements.

DETAILED DESCRIPTION

1 denotes a circular rotatable knob or rotor having a downwardly facinghollow space 8 wherein a permanent magnet 2--in the figure a rodmagnet--is arranged. In its mounted position, the rotor 1 engages in aknown manner and by means of an inwardly facing flange 9 with acorresponding outwardly Facing flange 10 on a base portion or stator 3,in the internal upwardly facing hollow space 11 of which a soft-irondisc 5 is mounted and immediately on top of the disc an integratedcircuit 4 having magnetic field sensitive elements 14 and associatedcircuitry 15, is mounted. To peripheral areas of the circuit, a total offour terminals 6 are mounted by tape automated bonding (TAB) and thus inelectrically conductive connection thereto, said terminals 6 beingembedded in the hollow space 11 of the stator 3 together with thecircuit 4 and the iron disc. The terminals 6 are embedded in the statoror they extend through its wall through ducts or notches 7.

When the rotor 1 with the magnet 2 is rotated relative to the stator 3with the integrated circuit 4, which rotation may he effected freely inboth directions within a rotational range determined by the mechanicalstop 13 and the groove in the knob 12, the position change of the magneteffected is sensed by the magnetic field sensitive elements of thecircuit and is converted as disclosed above to a digital code which istransmitted to a computer in a not shown hearing aid of which theposition sensor is a part. The computer converts the code signalreceived to the desired function in the apparatus, e.g. to increase orreduce the volume.

I claim:
 1. A microelectronic position sensor for determining changes in an adjustable parameter of an apparatus, said position sensor comprising:a stationary base portion including magnetic field sensitive elements and an adjustment means rotatably mounted within said adjustment means and including a permanent magnet; said adjustment means being electrically coupled to the apparatus by means of a plurality of electrically conductive terminals embedded in said adjustment means; said adjustment means comprising an integrated circuit on which said magnetic field sensitive elements are mounted for providing an electrical signal depending on the position of the permanent magnet and the rotor; said adjustment means and said stationary base portion comprise housing parts having interengaging flanges and forming together a self-contained unit encompassing the electric and and magnetic components of the position sensor and in which the adjustment means is rotatably mounted on the stationary base member; a soft-iron member is mounted in the stationary base member to form an iron return path the magnetic system comprising the permanent magnet and the magnetic field sensitive elements; and the electrically conductive contact between the terminals and the integrated circuit is effected by bonding to the integrated circuit, each terminal being separately secured to the integrated circuit.
 2. A microelectronic position sensor as claimed in claim 1, wherein said permanent magnet is shaped to obtain an optimum field variation.
 3. A microelectronic position sensor as claimed in claim 1, wherein the said stationary base portion includes a mechanical stop for the rotation of said adjustment means.
 4. A microelectronic position sensor as claimed in claim 11 wherein said integrated circuit includes a plurality of circularly positioned magnetic field sensitive elements. 